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Microbial Nutrition

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Last revised: Monday, February 7, 2000
Ch. 5 in Prescott et al, Microbiology, 4th Ed.
Note: These notes are provided as a guide to topics the instructor hopes to cover during lecture. Actual coverage will always differ somewhat from what is printed here. These notes are not a substitute for the actual lecture!
Copyright 2000. Thomas M. Terry

Nutritional categories

  1. Energy source
    1. if organic molecules (e.g. sugars, amino acids) = ORGANOTROPH
    2. if inorganic molecules (e.g. H2S, NH3) = LITHOTROPH
    3. if light = PHOTOTROPH
  2. Macronutrients: Cell requires ~ 30 elements. Needs 6 in large amounts (CHNOPS), some only in trace amts, some in between
    1. C-source
        1. can be CO2 = AUTOTROPH
        2. can be organic molecules = HETEROTROPH
      • Note: many bacteria can form all organic molecules from any of a wide variety of C-sources. E.g., Pseudomonas strains (soil organisms) can grow on hydrocarbons, variety of sugars, fats, polysaccharides, etc.
      • Full description of microbe typically refers to both E- and C-source; lithotrophic autotroph (chemolithotroph); organotrophic heterotroph, etc. Will see many examples of these.
    2. N-source
      • Typical bacterium is 15% nitrogen (in proteins, nucleic acids, cell wall).
      • Most bacteria obtain either amino groups (-NH2) or ammonia (NH3), or nitrate (NO3--).
      • Some bacteria can fix atmospheric nitrogen (N2) to form ammonia (NH3)
    3. P-source
      • generally available as phosphate ion (PO4---) or organic molecules (e.g. RNA).
      • Often limiting for growth.
    4. S-source
      • required for 2 amino acids and for some vitamins.
      • Available as sulfate (SO4--) or sulfide (S--).
  3. Micronutrients
    • K, Mg, Ca, Fe required in small but significant amts. Act as cofactors for many enzymes, cell structures (e.g., Mg++ required by ribosomes for protein synthesis).
    • Na+ not required by many microbes (unlike animals, where nerve system requires Na+ and K+). Marine microbes require sodium.
    • Trace elements: Co, Zn, Mo, Cu, Mn, Ni, W, Se -- usually required by a small number of enzymes.

Membrane transport

  1. Varieties of transport proteins:
    1. Uniporter -- protein transports substrate from one side of membrane to other (Passive transport -- no energy required)
    2. Symporter -- protein carries two substances across membrane in same direction (e.g. proton flux is coupled with motion of substrate). Active transport -- requires energy from preexisting concentration gradient.
    3. Antiporter -- protein carries one substance in one direction, second substance in opposite direction. Active transport -- requires energy from preexisting concentration gradient.
  2. Specific examples of transport processes
    1. Group translocation -- substance is chemically altered while being transported.
      • Example: phosphotransferase system used in sugar transport. Sugars are common energy sources, bacteria have evolved complex transport system to bring them across membrane whenever possible.
      • In E. coli, 24 proteins involved, can transport a variety of sugars (at least 4 proteins needed for any given sugar).
      • Mechanism involves alternate phosphorylation (adding Pi group) and dephosphorylation (removing Pi group) of series of carriers. Initial phosphate donor is high-energy molecule PEP, passes Pi group to Enzme I --> HPr protein Enzyme IIa Enzyme IIb Enzyme IIc. Only the very last of these proteins is located in membrane; others are all found in cytoplasm. Sugar (e.g., glucose) is carried into cell by Enzyme IIc, and at same time phosphate group is added to make glucose 6-P, hence group translocation (sugar is modified by added Pi group)
    2. Active Transport -- substance is imported without chemical change, and energy is expended.
      • Energy may be used in form of ATP
      • More commonly, cells use energy in form of proton gradient or ion gradiend such as sodium gradient. After proton gradient is established (to be discussed later in section on energetics), symport proteins allow substate to brought in along with entry of proton.

Culture Media

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